Solid imaging apparatus having a semi-permeable film

ABSTRACT

An apparatus for fabricating integral three-dimensional objects from successive layers of photoformable compositions by exposing the layers of the composition through a semi-permeable film that allows creation of release coatings on the side of the film facing the composition.

This is a division of application Ser. No. 07/604,982, filed Oct. 29,1990, now U.S. Pat. No. 5,122,441.

FIELD OF THE INVENTION

This invention relates to production of three-dimensional objects byphotoforming, and more particularly to the controlled application ofthin flat liquid layers accurately and quickly to a platform orpreviously photoformed layer(s) to accomplish said production withlayers of improved flatness, accuracy and integrity.

BACKGROUND OF THE INVENTION

Many systems for production of three-dimensional modeling byphotohardening have been proposed. European patent application 250,121filed by Scitex Corporation, Ltd. on Jun. 6, 1987, discloses athree-dimensional modeling apparatus using a solidifiable liquid, andprovides a good summary of documents pertinent to this art.

These approaches relate to the formation of solid sectors ofthree-dimensional objects in steps by sequential irradiation of areas orvolumes sought to be solidified. Various masking techniques aredescribed as well as the use of direct laser writing, i.e., exposing aphoto-hardenable composition with a laser beam according to a desiredpattern and building a three-dimensional model layer by layer. Inaddition to various exposure techniques, several methods of forming thinliquid layers are described which allow either the coating of a platforminitially or the successive coating of object layers previously exposed.

U.S. Pat. No. 4,575,330 (C. W. Hull), issued on Mar. 11, 1986 and laterreexamined (certificate issued on Dec. 19, 1989), describes a system forgenerating three-dimensional objects by creating a cross-sectionalpattern of the object to be formed at a selected surface of a fluidmedium capable of altering its physical state in response to appropriatesynergistic stimulation by impinging radiation, particle bombardment orchemical reaction, wherein successive adjacent laminae, representingcorresponding successive adjacent cross-sections of the object, areautomatically formed and integrated together to provide a step-wiselaminar buildup of the desired object, whereby a three-dimensionalobject is formed and drawn from a substantially planar surface of thefluid medium during the forming process. This patent also describes anembodiment in which a UV curable liquid floats on a heavier UVtransparent liquid which is non-miscible and non-wetting with thecurable liquid. In addition, this patent suggests the use of "water (orother) release coating" used in conjunction with a CRT and a fiber opticfaceplate. Subsequent patent applications, made by Hull and hisassociates, published by the European Patent Office and listed inpublication number 0 361 847 describe means of providing the thin layersof fluid more quickly using a doctor blade and of controlling the levelin a vat of fluid.

U.S. Pat. Nos. 4,752,498 and 4,801,477 (E. V. Fudim) issued on Jun. 21,1988 and Jan. 31, 1989 respectively, describe methods of formingthree-dimensional objects, in which a sufficiently rigid transparentplate or film is placed in contact with a liquid photopolymer so as tohold the photopolymer surface to a desired shape, and preferably excludeair, during radiation curing through the transparent plate or film. Itis further suggested that the surface of the transparent plate or filmbe made of a material which leaves the irradiated photopolymer surfacecapable of further crosslinking so that when a subsequent layer isformed it will adhere thereto. Fudim also suggests that this material bemade of or contain in it's molecules oxygen, copper or other inhibitorsto aid in the release of the layer without distorting the solidifiedphotopolymer.

Publication "Automatic Method for Fabricating a Three-DimensionalPlastic Model with Photohardening Polymer" by Hideo Kodama, Rev. Sci.Instrum. 52(11), 1770-1773, Nov. 1981, describes a method for automaticfabrication of a three-dimensional plastic model. The solid model isfabricated by exposing liquid photo-forming polymer, of 2 mm thicknessor less, to ultraviolet rays, and stacking the cross-sectionalsolidified layers. Publication "Solid Object Generation" by Alan J.Herbert, Journal of Applied Photographic Engineering, 8(4), 185-188,August 1982, describes an apparatus which can produce a replica of asolid or three-dimensional object much as a photocopier is capable ofperforming the same task for a two-dimensional object. The apparatus iscapable of generating, in photopolymer, simple three-dimensional objectsfrom information stored in computer memory. A good review of thedifferent methods is also given by a more recent publication, titled "AReview of 3D Solid Object Generation" by A. J. Herbert, Journal ofImaging Technology 15:186-190 (1989).

Most of these approaches relate to the formation of solid sectors ofthree-dimensional objects in steps by sequential irradiation of areas orvolumes sought to be solidified. Various masking techniques aredescribed as well as the use of direct laser writing, i.e. exposing aphotoformable composition with a laser beam according to a desiredpattern and building a three-dimensional model layer by layer. Inaddition to various exposure techniques, several methods of forming thinliquid layers are described which allow both coating a platforminitially and coating successive layers previously exposed andsolidified.

Current methods of coating suggested thus far, however, have drawbacksin that they are not capable of ensuring flat uniform layer thickness orof producing such layers quickly, or they do not effectively preventdamage to previously formed layers during the successive coatingprocess. Furthermore, they omit to recognize very important parametersinvolved in the coating process such as, for example, the effects ofhaving both solid and liquid regions present during the formation of thethin liquid layers, the effects of fluid flow and theologicalcharacteristics of the liquid, the tendency for thin photoformed layersto easily become distorted by fluid flow during coating, and the effectsof weak forces such as, for example, hydrogen bonds and substantiallystronger forces such as, for example, mechanical bonds and vacuum orpressure differential forces on those thin layers and on the objectbeing formed.

The Hull patent, for example describes a dipping process where aplatform is lowered either one layer thickness or is dipped below thedistance of one layer in a vat then brought up to within one layerthickness of the surface of the photohardenable liquid. Hull furthersuggests that low viscosity liquids are preferable, but for otherpractical reasons, the photohardenable liquids are generally highviscosity liquids. Although theoretically most liquids will flatten outdue to surface tension effects, high viscosity liquids and even lowviscosity liquids take an inordinate amount of time to flatten to anacceptable degree especially if large flat areas are being imaged and ifthe liquid layer thickness is very thin. Regions where previous layersconsist of solid walls surrounding liquid pools further compounds theflattening process of the thin liquid layer coating. In addition, motionof the platform and parts, which have cantilevered or beam (regionsunsupported in the Z direction by previous layer sections), within theliquid creates deflections in the layers contributing to a lack oftolerance in the finished object. In the embodiment where a heaviertransparent liquid is utilized to create the thin flat layers ofphotopolymer that float on the transparent liquid, there is significantreliance on surface tension effects to ensure that the photopolymerlayer will be flat. Reliance on these surface tension effects and thedifference in specific gravities between the two liquids in order tocreate the flat photopolymer layers is severely complicated by othersurface tension effects, such as, for example, meniscus development atthe corners of the hardened photopolymer, and object geometries thatcreate enclosed areas which produce substantial suction cup type liftingof the heavier liquid during coating of subsequent layers. In theembodiment where "water (or other) release coating" is proposed for usein-conjunction with a CRT and a fiber optic faceplate, the patent doesnot teach methods by which a release coating could be applied andmaintained on the faceplate surface.

The Munz patent (U.S. Pat. No. 2,775,758 issued in 1956) and Scitexapplication describe methods by which the photohardenable liquid isintroduced into the vat by means of a pump or similar apparatus suchthat the new liquid level surface forms in one layer thickness over thepreviously exposed layers. Such methods have all the problems of theHull methods except that the deflections of the layers during coating isreduced.

The Fudim patent describes the use of a transmitting material, usuallyrigid and coated with a film or inherently unlikely to adhere to thehardened photopolymer, to fix the surface of the photopolymer liquid toa desired shape, assumably flat, through which photopolymers of desiredthickness are solidified. The methods described by Fudim do not addressthe problems inherent-in separating such a transmissive material from aphotopolymer formed in intimate contact with the surface of thetransmissive material. Whereas the effects of chemical bonding may bereduced significantly by suitable coatings of inherently suitable films,the mechanical bonds along with hydrogen bonds, vacuum forces, and thelike are still present and in some cases substantial enough to causedamage to the photopolymer during removal from the transmissive materialsurface. Furthermore, evaluations made by the Applicants indicate thatthe forces, resisting the separation or even sliding off thephotohardenable material exposed in intimate contact with the suitablynon-adhesive transmissive material, are capable of damaging thephotoformed layer especially when surrounded by photohardenable liquidand even more especially when the photoformed layers are thin. No methodis described in the Fudim patent to eliminate these problems.

In the Kodama (Kokai Patent No. SHO 56(1981)-144478, Japan, laterpublished on Nov. 10, 1981) publication, mention is made of a Teflon, orpolyethylene coated quartz plate, which coating acts as a releasingagent allowing the solidified resin to be easily removed from the base(quartz plate) and preferentially adhering to the constructing stand(aluminum sheet). This method would have all the difficulties mentionedin the Fudim reference above.

While it may be said that others such as Munz, Kodama, Cubital, Hull,etc. implicitly had air as the atmosphere at the interface of thephotopolymer surface, air was not an element comprised within theirspecifications. And the presence, advantages, and uses of air in regionsdeeper into the compositions (also implicit in previous specifications)has not been specified though they are implicit.

In a thesis paper, published by the Department of MechanicalEngineering, University of Delaware, library catalogue date Aug. 14,1990, there is mention of an unsuccessful effort, in which the author,Hirsch, studied the possibility of creating a porous fused silica platethrough which the photopolymer could be exposed. The purpose of theporosity in the plate was to allow air to flow into the surface betweenthe plate and the hardened layer to allow vacuum breaking when they wereseparated. It was also proposed that the air or oxygen passing throughthe plate might inhibit the polymerization at this surface aiding inrelease. This effort was unsuccessful primarily due to difficulties inobtaining a UV transparent porous plate material. But it also neglectsconcerns such as, for example, polymer adhesion to the fused silica innon-pore regions and eventual bridging of this polymer in subsequentcoating applications which would close off the pores, the requirementfor very small pore sizes which would severely restrict the air flowwhich is supposed to relieve the vacuum forces, and the lack of anydriving forces or pressures to prevent the photopolymer from enteringthe pores or to push the air into the interface between the porous plateand the photopolymer surface.

One of the objects of the present invention is therefore to provide amethod and apparatus for quickly producing layers of a liquidphotoformable material, of preferably 0.030" thickness or less, whichare flat to within preferably 0.001" per square inch or better, and bywhich previously exposed layers are minimally distorted or damagedduring the coating process for the production of three-dimensionalobjects by sequential coating of said layers and exposure after eachcoating.

SUMMARY OF THE INVENTION

This invention provides unique solutions to these problems by utilizinga semi-permeable film, which is impermeable to the photoformablecomposition but is permeable to a deformable-coating-mixture that isnon-wetting and immiscible with the photoformable composition. Thedeformable-coating-mixture passes through the membrane preferably bydiffusion effects and forms a thin, slippery surface on thephotoformable composition side of the membrane, thereby eliminating anyadhesion forces caused by chemical, mechanical or hydrogen bonds and thelike. Also this invention teaches of methods by which dissolvedinhibitors can be used within the deformable-coating-mixtures and withinthe composition to provide improved interlayer adhesion and gentlercoating. Furthermore, this invention teaches of methods by whichrecesses or large orifices can be created, between the film andpreviously formed layers, through which the photoformable compositionmay be caused to flow, thereby substantially alleviating vacuum forcesthat may arise during separation of the film from the photoformed layer.

A method for fabricating an integral three-dimensional object fromsuccessive layers of a photoformable composition comprising the stepsof:

a) positioning a substantially transparent, composition-impermeable,composition-inert, semi-permeable film, having a first surface and asecond surface, such that said film first surface is, at leastpartially, in contact with an imaging atmosphere, and said film secondsurface is, at least partially, in contact with the photoformablecomposition;

b) contacting an interface of said composition with a compositionatmosphere;

c) allowing said imaging atmosphere to permeate through said film andpartially into a photoformable-composition-layer;

d) exposing said photoformable-composition-layer to radiation imagewisethrough said film making a photoformed layer and adeformable-composition-release-coating;

e) sliding said film from said photoformed layer;

f) positioning said film in such a way as to form aphotoformable-composition-layer between said previously made photoformedlayer and said film second surface; and

g) repeating steps c-f until said layers of the integralthree-dimensional object are formed.

Single layers may be fabricated as above by performing the steps a-eabove.

BRIEF DESCRIPTION OF THE DRAWINGS

The reader's understanding of practical implementation of preferredembodiments of the invention will be enhanced by reference to thefollowing detailed description taken in conjunction with perusal of thedrawing Figures, wherein:

FIG. 1 depicts the major elements in an embodiment of the inventionduring the imaging step.

FIG. 2 depicts a preferred embodiment of the invention during theprocess of sliding the imaged layers in preparation for anotherphotoformable-composition-layer.

FIG. 3 depicts an embodiment utilizing a porous plate with a partiallyadhered semi-permeable film in the process of separating the film andcoating from the photoformed layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention relates to a process and apparatus for producingthree-dimensional objects by photoforming, and more particularly to theuse of semi-permeable films and coatings useful for providing a releasemechanism from photoformed layers during the formation process.

The readers appreciation and understanding of the inventions describedherein will be enhanced by reference to the drawings and a descriptionof the drawings and operation described below.

In reference now to FIG. 1, there is provided a semi-permeable film 102,having first and second surfaces, positioned in a photoformablecomposition 104 by tenter frame 106 in such a manner that the filmsecond surface 102" is in contact with the photoformable composition 104and the film first surface 102' is facing away from the composition 104.The film 102 is held to a particular shape by placing it in a tenterframe 106. A deformable-coating-mixture 110' with a dissolved inhibitor142' is introduced on the film first surface 102' side. Also, apermeated-deformable-release-coating 110 with a permeated inhibitor 142is between the film second surface 102" and aphotoformable-composition-layer 112. Thisphotoformable-composition-layer 112 may contain different concentrationsthan that of photoformable composition 104 due to, for example,dissolved inhibitor 142' diffusing through the semi-permeable film 102.For the purposes of this invention, a deformable release coating shallmean a coating, of one molecular thickness or more, that is a gas, aliquid, and/or a gel such that its shape may be changed by theapplication of pressures or forces. Similarly, a photoformablecomposition is a material which is a liquid and/or a gel, which maycontain dissolved gases, and which, photoforms, hardens or increases inviscosity when exposed to appropriate sources of radiation. A radiationsource 114 illuminates specific regions ofphotoformable-composition-layer 112 through a photomask 116 causing thephotoformable-composition-layer 112 to harden. Afterphotoformable-composition-layer 112 is photoformed, creating photoformedlayer(s) 122, radiation source 114 is turned off or shuttered and tenterframe 106 and film 102 are slid from the surface of photoformed layer122 by frame assembly translation means 118 (shown in FIG. 1 as an arrowfor the sake of simplicity). Then the platform 120 and the previouslyphotoformed layer(s) 122 are translated at least onephotoformable-composition-layer thickness relative from the originalsurface of film 102 and permeated-deformable-release-coating 110 byplatform translation means 124. After the previously photoformedlayer(s) 122 have been translated by platform translation means 124,frame assembly translation means 118 moves the film 102 and tenter frame106 back into substantially it's original position, moving asidephotoformable composition 104 and forming a newphotoformable-composition-layer 112. This process is continued until thedesired three-dimensional object is imaged. In the embodiment shown inFIG. 1, the photoformable composition 104 is contained in a vat 126. Thephotoformable composition 104 forms a composition/atmosphere interface153. Above this composition/atmosphere interface, there is a compositionatmosphere 152. Above the film 102 held to a shape by the tenter frame106 and the deformable-coating-mixture 110', there is an imagingatmosphere 156 which may be different from the composition atmosphere152.

FIG. 2 depicts a preferred embodiment of the instant invention. In thisembodiment there is a semi-permeable transparent film 202, having firstand second surfaces, with the film second surface 202" facing thephotoformable composition 204 and the film first surface 202' facing atransparent plate 232. The transparent plate 232, having first andsecond faces 232' and 232" respectively, has the first plate face 232'facing the composition 204 and the second plate face 232" facing awayfrom the composition 204. The film 202 is stretched to conform to theshape of the plate 232 and both film 202 and plate 232 are secured in aframe 207, which also serves as a composition 204 vat, by compressionflange 234 using securing means (screws, levers, etc. not shown forclarity) such that the film 202 and plate 232 are sealed and thephotoformable composition 204 does not leak from the frame 207 betweenthe film 202 and the frame 207, and pressures can be maintained withoutleakage between the film 202 and the plate 232. Adeformable-coating-mixture 210' is introduced between the film 202 andthe plate 232 through first tube 230' and second tube 230" which aresealed to the plate 232 in a manner adequate to prevent leakage. Firstand second tubes 230' and 230" are connected respectively to a firstreplenishment assembly 254' and a second replenishment assembly 254",each of which comprise respectively a porous tube 238, a tube screen240, a concentrated inhibitor 242", dissolved inhibitor 242', transfersolution 211, a flask 246, and an inhibitor supply 244. The porous tubes238 in first and second replenishment assemblies 254' and 254" areconnected to each other through flexible tube 258. The flexible tube 258is squeezed by squeeze roller 236 against a portion of frame 207 in sucha manner that the flexible tube 258 is divided preventing thedeformable-coating-mixture 210' and any dissolved inhibitor 242' fromflowing through the squeeze point 237. The deformable-coating-mixture210' along with dissolved inhibitor 242' permeates through the film 202forming a permeated-deformable-release-coating 210 with permeatedinhibitor 242 on the film second surface 202" between the film 202 andthe composition 204. In plate 232 there is a recess region 228. Wedge248 is secured in this recess region 228 in such a manner as to dividethe film 202 secured between the plate 232 and frame 207 into twochambers, first chamber 250' and second chamber 250". Above the frame207 there is a composition atmosphere 252. The frame assembly(comprising frame 207, plate 232, first and second chambers 250' and250", composition 204, compression flange 234, first and second tubes230' and 230", recess 228, wedge 248 and portions of flexible tube 258)are moved relative to the squeeze roller 236 the radiation source 214,the photomask 216, the photoformed layers 222, the platform 220, and theplatform translation means 224, in a direction substantially parallel tothe first plate face 232' by frame assembly translation means 218.Platform translation means 224 translates the platform 220 and anyphotoformed layers 222 in a direction substantially normal to the firstplate face 232'. When the platform 220 or previously photoformed layers222 creates a region of photoformable composition 204 one layerthickness between the platform 220 or the photoformed layer(s) 222 andthe permeated-deformable-release-coating 210, in preparation forexposure by radiation source 214 through photomask 216, aphotoformable-composition-layer 212 exists. Thisphotoformable-composition-layer 212 may contain different concentrationsthan that of photoformable composition 204 due to, for example,dissolved gases or inhibitors 242 diffusing through the coating 210 intophotoformable-composition-layer 212.

The operation of the apparatus in FIG. 2 is as follows:

Photoformable composition 204 is placed in the frame 207. It is notnecessary that frame 207 be leveled, relative to earth's gravity, exceptto prevent the composition 204 from flowing over the frame 207 sides. Itis only necessary to provide enough composition 204 in frame 207 toensure that a complete object can be made and that compositionatmosphere 252 bubbles are not introduced between the platform 220 andthe plate 232 during translation by translation means 218 or 224. Ifnecessary, photoformable composition 204 refill means (not shown) may beprovided. Chambers 250' and 250" are filled withdeformable-coating-mixture 210' and dissolved inhibitor 242' in a mannersuch that when one chamber, for example first chamber 250', has thedeformable-coating-mixture 210' and dissolved inhibitor 242' being drawnfrom it, second chamber 250" has the deformable-coating-mixture 210' anddissolved inhibitor 242' entering it. This is due to the pumping, actionof squeeze roller 236 rolling and squeezing flexible tube 258 againstframe 207 as frame assembly translation means 218 translates the frameassembly (comprising items described above), thereby changing the volumeof flexible tubing 258 connected as described above to first and secondchambers 250' and 250". As shown, therefore, as the frame assembly(comprising items described above) is translated by frame assemblytranslation means 218 to the right, squeeze roller 236 squeezes andreduces the volume of flexible tube 258 connected through secondreplenishment assembly 254" and second tube 230" to second chamber 250".The deformable-coating-mixture 210' and dissolved inhibitor 242' therebyflows into second chamber 250" causing it to bulge. In the preferredembodiment, film 202 is elastomeric and therefore is capable of bulgingor flattening without permanent deformation. On the other side, whilethe frame assembly (comprising items described above) moves to theright, the volume, in flexible tubing 258 connected through firstreplenishment assembly 254' and first tube 230' to first chamber 250',increases, thereby drawing deformable-coating-mixture 210' and dissolvedinhibitor 242' from the first chamber 250' and causing the film 202 toflatten on this side. As the frame assembly (comprising items describedabove) is moved to the left the volume changes, thedeformable-coating-mixture 210' flow, and the bulging/flatteningrelationships between first and second chambers 250' and 250" would bereversed. As the frame assembly (comprising items described above) movesand pumps the deformable-coating-mixture 210' and dissolved inhibitor242' into or out of the first and second chambers 250' and 250" thedeformable-coating-mixture 210' and dissolved inhibitor 242' passthrough the, first and second replenishment assemblies 254' and 254"respectively. Within said first and second replenishment assemblies 254'and 254", a porous tubing 238 contains the flow of coating mixture 210'and 242' while allowing concentrated inhibitor 242" to pass by diffusionmeans into the deformable-coating-mixture 210'. The porous tubing 238,further described later, is such that it can substantially contain arelative pressure but may collapse when containing a relative vacuum.The tube screen 240 prevents the collapse of porous tubing 238 when arelative vacuum is being maintained. Since during the photoformationprocess further described, permeated inhibitor 242 is consumed, therewill be diffusion of dissolved inhibitor 242' through the film 202 fromthe deformable-coating-mixture 210' thereby decreasing its concentrationof dissolved inhibitor 242'. In the replenishment assemblies 254' and254" inhibitor supply 244 maintains the concentration of concentratedinhibitor 242" at a relatively high level in the transfer solution 211within the flask 246. Therefore, diffusion and the flow ofdeformable-coating-mixture 210' and dissolved inhibitor 242' (due tovolume changes in flexible tubing 258 as described above) through poroustube 238 causes the concentrated inhibitor 242" to replenish the lowconcentration of dissolved inhibitor 242', which in turn permeatesthrough film 202, replenishing the concentration of permeated inhibitor242, and which in turn diffuses into the photoformable-composition-layer212.

In preparation for making photoformed layer(s) 222, for example, theframe assembly (comprising items described above) is moved to the rightby frame assembly translation means 218 such that platform 220 is facinga flat region of the plate first face 232'. The platform 220 istranslated by platform translation means 224 to a position such that aphotoformable-composition-layer 212 is formed. Radiation source 214 andphotomask 216 are positioned such that they can shine substantiallycollimated illumination, through the plate 232 (The reader shouldunderstand that the only thing substantially limiting illumination ofthe plate 232 by radiation source 214 is photomask 216.),deformable-coating-mixture 210' and dissolved inhibitor 242', film 202,and permeated-deformable-release-coating 210 and permeated inhibitor242, into photoformable-composition-layer 212. An imagewise exposure ismade that is substantial enough to create a photoformed layer 222portions of which substantially adhere to platform 220. Preferablyplatform translation means 224 translates the platform 220 and anyattached photoformed layer 222 the distance of onephotoformable-composition-layer away form plate 232. This usually causesthe film 202, the permeated-deformable-release-coating 210, thepermeated inhibitor 242, the deformable-coating-mixture 210', anddissolved inhibitor 242' to substantially rise also, overcoming therelative vacuum formed in flexible tubing 258. Next or simultaneously,frame assembly translation means 218 translates the frame assembly(comprising items described above) to the left. As this occurs, portionsof photoformed layer 222 reach the edge of recess 228 where the film 202and permeated-deformable-release-coating 210 substantially separate fromthe photoformed layer 222. Photoformable composition 204 flows withsubstantial ease through recess 228 to fill the gap at the separationline between the photoformed layer 222 and film 202. When thephotoformed layer 222 passes over the right edge of recess 228 a newphotoformable-composition-layer 212 is created above the second chamber250". As this occurs, second chamber 250" collapses (for reasonsdescribed above) causing film 202 and the coating mixtures to conform tothe substantially flat shape of plate 232 in this region. From thispoint, another imagewise exposure can be made substantial enough toadhere portions of the newly photoformed layer 222 to the previousphotoformed layer(s) 222. The process above can be repeated, coatingphotoformable composition 204 on one side and exposing imagewise on thesame side then separating the photoformed layers 222 from the film 202,etc. until all photoformed layers 222 have been fabricated necessary forthe production of an object.

It is preferred that the film be-impermeable to the photoformablecomposition and substantially inert to it. The impermeability preventsthe composition from passing from the composition contacted surface ofthe film to the other surface, or into the pores of the film, where theradiation would photoform it. Examples of such films may be composed ofpolypropylene (such as, for example, film manufactured by Hercules Inc.Wilmington DE), Teflon PFA®, Teflon TFE® (such as, for example,manufactured by E. I. DuPont De Nemours Inc., Wilmington Del.), orpolyethylene, etc. or any of a number of polymer and copolymer films.Some films such as, for example, molecularporous membranes (such as, forexample, those manufactured by Spectrum Medical Industries, Los Angeles,Calif.), may prove suitable for some applications of the invention inthat they have a known pore size that allows molecules of low molecularweight to pass through the film while molecules of a size larger thanthe pore size cutoff are prevented from passing through the film. Forsuch an application, it would be desirable for the molecular size of thecomposition to be larger than the pore size and for the molecular weightof a deformable-coating-mixture (such as will be described later) anddiffused inhibitors to be of smaller molecular size than the pore size.In this case, a deformable-coating-mixture can pass through the film by,for example capillary action. In the case of FIG. 2, the preferredporous tubing 238 is, for example, Spectra/Por molecularporous membranetubings which have molecular weight cutoffs in the range of 100 to 500.These porous tubes 238 can withstand fairly high pressures and arecapable of diffusing concentrated inhibitors 242", for exampleconcentrated oxygen, without substantially diffusing the transfersolution 211 or deformable-coating-mixture 210'. Still more preferableis a film that is of substantially different molecular polarity thanthat of the photoformable composition or that of the photoformed layerssuch that the composition and the photoformed layers tend not to wet thefilm. This is advantageous for several reasons: Lack of wetting of thefilm by the composition decreases the potential for bonding to the filmduring photoforming of the composition. And, since all films are porousto some degree or molecular size, lack of wetting by the compositionsignificantly decreases its permeation of the film since surface tensioneffects tend to prevent the composition from entering or passing throughthe pores. (Such art is the basis of many products, for example,Goretex® manufactured by Gore Associates Inc., Newark, Del.).

Preferably, the film is held submerged in the photoformable compositionand held substantially to a particular shape, preferably substantiallyflat, by placement of a transparent plate against the film surface thatis opposite the photoformable composition. In the preferred mode, shownin FIG. 2, in which UV light is the preferred radiation source 214, theplate 232 usually is made of, for example, quartz, fused silica,waterwhite glass, or any other material that is substantiallytransparent to the wavelength in use and has substantially good opticalqualities. For other forms of radiation such as, for example, microwaveor dielectric excitation, plastics or even metals may provide suitableplate material if they are substantially transparent to the radiationand if they induce substantially low distortion of the electromagneticfields. Or, as in the case of FIG. 1, the film 102 may be held to aparticular shape by use of a tenter frame 106, or the film 102 may evenpossess the desired shape and necessary stiffness to obviate the needfor a frame 106. For the purposes of this invention, referring now toFIG. 2, a substantially flat plate 232 in contact with the film 202 ispreferred, however, the plate 232 may have any curvature that allowssliding of the film 202 from the photoformed surface 222 and does notcreate damaging vacuum forces between the film 202 and the photoformedlayer 222 during the sliding action. The film 202 is preferably pulledby vacuum means (combination of 218, 236 and 258 as described above) toensure it conforms substantially to the shape of the plate 232 itcontacts. The plate 232 may be of any useful size necessary for theproduction of large or small photoformed layers. The plate may also be,for example, an optical fiber.

For the purposes of the instant invention, it is preferred that the filmbe an elastomeric film since such films conform more readily to theshape of any desired surface and these films, such as, for example,silicone, tend to have high diffusion coefficients even though themolecular size of the penetrant molecule is greater than the pore orhole size. A penetrant molecule can often temporarily expand holes infilms if the films have polymer chain mobility. Thus the penetrant canmove the polymer chains aside and squeeze through the expanded holes orpores. Elastomeric films typically have even greater chain mobilityenhancing the ability of the penetrant to expand the holes and thereforeincreasing the diffusion of the penetrant. Further enhancing thispenetration is the presence of a plasticizer, such as for example adeformable-coating-mixture, which increases the film chain mobility andcreates swelling, thus allowing easier permeation of the penetrantthrough the film.

Preferred elastomeric films are, for example, transparent siliconeelastomers and fluoroelastomers, such as for example clear Kalrez®, soldby DuPont. Most preferable are fluoroelastomers. A film of this type,which was extensively used during this work, was prepared as follows:

(A) a 10 gallon stainless steel autoclave was evacuated and purged withnitrogen and then was charged with 2600 liters of deionized,de-oxygenated water containing 1.5 liters of Freon 113 (1,1,2 trichloro,1,2,2 trifluoro ethane), and in which was dissolved 56 g. of ammoniumperfluorooctanoate surfactant (FC-143, 3M Co.). The reactor was thenpressured to about 0.2 MPa (30 psi) with the "start-up monomer" mixturewhich had the following composition: 30% by weight TFE(tetrafluoroethylene) and 70% by weight PMVE (perfluoro (methyl vinylether)). The autoclave was vented off to about 0.03 MPa (5 psi). Thepressuring and venting was repeated 2 more times. At this time, 3.6 g of1,4 diodoperfluorobutane, dissolved in 36 ml of 1,1,2 trichloro 1,2,2trifluoroethane, was added, and the autoclave was heated to 80° C. whilestirring at 125 rpm. The autoclave was then pressured to 2.1 MPa (300psi) with the "start-up monomer" mixture described above. To start thepolymerization, the autoclave was charged with 20 ml of a 2% solution ofammonium persulfate in water. After the pressure in the autoclave haddecreased to about 2.0 MPa (295 psi). The autoclave was maintained at apressure of about 2.1 MPa (300 psi), during the course of thepolymerization, by regular addition of the "make-up monomer" mixture.The "make-up monomer" mixture had the following composition: 46% byweight TFE, 8% by weight ethylene, and 46% by weight PMVE. Thepolymerization was allowed to continue for a total of 15 hours duringwhich time 6500 grams of the make-up monomer mixture was added. Also,during this period an additional 129 ml of 1% ammonium persulfate wasadded in small increments. The unreacted monomers were vented from theautoclave and the polymer dispersion was discharged into a largecontainer. The pH of the dispersion was 2.7 and it contained 20.7%solids.

The fluoroelastomer was isolated from 500 ml of the above dispersion bycoagulating with potassium aluminum sulfate solution. The coagulatedpolymer was separated from the supernate by filtration and then washed 3times by high speed stirring in a large blender. Finally, the wet crumbwas dried in a vacuum oven at 70° C. for 40 hours. The recovered, drypolymer from the 500 ml aliquot weighed 114 grams. The composition ofthe fluoroelastomer was as follows: 45% by weight TFE, 6.8% by weightethylene, and 38.2% by weight PMVE. The polymer contained 0.22% iodineand had a Mooney viscosity, ML-10, measured at 121C. of 32.

(B) A 10 gallon autoclave was charged with 30 Kg of the polymerdispersion prepared in (A) above. The autoclave was then evacuated andpurged 3 times with nitrogen, then 3 times with a new "start-up" monomermixture of the following composition: 90% by weight TFE and 10% byweight ethylene. The autoclave was then heated to 80° C. and pressuredto 1.3 MPa (190 psi) with the new "start-up monomer" mixture. Thepolymerization was then initiated by addition of 20 ml of 1% ammoniumpersulfate solution. The pressure was kept constant by addition of a new"make-up monomer" mixture which had a composition of 80% by weight TFEand 20% by weight ethylene. A total of 1050 g of the new "make-upmonomer" mixture was added in a 4.3 hour reaction time. The monomerswere then vented off and the segmented polymer dispersion was dischargedfrom the reactor. The dispersion contained 26.8% solids. The segmentedpolymer was isolated from the dispersion in the same manner as describedfor the fluorelastomer in (A) above. A total of 8.3 Kg of polymer wasrecovered.

Differential Scanning Calorimetry testing on the segmented polymerindicated a glass transition temperature of -14° C. for thefluoroelastomer segment and a melting point of 233° C. for thethermoplastic segments. The iodine content of the polymer was 0.13%. Themelt index (ASTM D-2116 using a 5 kg weight at 275° C.) was 3.0 g/10min.

A compression molded film of the polymer had M100 (modulus at 100%elongation) of 3.4 MPa (500 psi), tensile strength (break) of 23.4 MPa(3400 psi) and elongation (break) of 380%.

The fluffy polymer recovered according to the above procedure wasextruded into beads (approx. 3 mm×6 mm) in a 28 mm twin screw extruderat 250° C. under nitrogen. The same type of extruder was then used at300° C. under nitrogen to extrude a film through a slit die on a castingdrum. The film thickness was 0.0115".

The Applicants suggest that an understanding of the following proposedconcepts will give the reader an appreciation of the novelty andadvantages of their invention. However, these proposed concepts shouldonly be taken as suggestions to the reader, and by no means, should theApplicants' proposals be construed as limiting in any way the breadthand scope of this invention.

A material which is in contact with a photoformable composition duringexposure might interfere with the cross-linking. If the material, forexample, a Teflon® film or a nitrogen atmosphere, is substantially inertto the photoforming process and is the only material in contact with thecomposition at the time of the exposure, it is likely that thecomposition will cross-link to a significant degree. The degree ofcross-linking is limited by, for example, the presence of an inhibitorin the composition, the lack of adequate radiation, an improperly mixedformulation, etc. However, assuming all these conditions are notpresent, the degree of cross-linking is often limited by, for example,the change in mobility of radicals within a increasingly more viscousmatrix. This is to say that even under the most ideal conditions, thedegree of cross-linking of, for example, a photoformed layer is often bynature incomplete. This incompleteness of cross-linking or presence ofactive sites, if it exists on the surface of a photoformed layer, mayprovide potential cross-linking sites to which a subsequentphotoformable-composition-layer may bond (by cross-linking). However, agreater degree of cross-linking or a lesser number of active sites onthe surface of a first photoformed layer, provides fewer cross-linkingsites for the bonding of subsequent photoformed layers to the firstlayer by cross-linking means. Therefore it is reasonable to assume thata film, for example Teflon®, or an imaging atmosphere, for examplenitrogen, which is substantially inert to the cross-linking, but by it'spresence in contact with the photoformable composition during exposure,tends to prevent inhibitors from contacting the composition during theexposure, will allow a greater degree of cross-linking, and thereforefewer active cross-linking sites to which subsequent photoformed layersmight adhere. In short, an inert material, whether a gas, a liquid, agel, or a solid, in contact with a photoformable composition duringexposure, may significantly interfere with the photoformed layer'sability to cross-link to subsequent photoformed layers.

If, on the other hand, a substantially inert film, for example the abovefluoroelastomer, or a permeated-deformable-release-coating, such as forexample FC-40 (described later), or an imaging atmosphere, which allowsthe presence of an inhibitor to be in contact with thephotoformable-composition-layer during exposure, is utilized, there willbe a lesser degree of cross-linking at the interface and there may bemore active sites present to which subsequent layers may bond. It shouldbe understood that the imaging atmospheres described may contain aninhibitor, such as for example oxygen. An inhibitor, whether from theatmosphere, inherent in the coatings, or inherent in the formulation ofthe photoformable composition, is free to diffuse into the compositionand change the composition concentration. The presence of inhibitorstypically decrease the degree of cross-linking by, for example,quenching an initiator or quenching a radicalized monomer. In manycases, the quenched initiators or quenched radicalized monomers are atleast partially no longer available to participate in a photo reaction.Therefore, quenched monomers immediately at an interface, where theinhibitor concentration is the highest, for example, at the interface ofthe permeated-deformable-release-coating within thephotoformable-composition-layer, are likely not to be cross-linked norare they usually considered to be active sites for subsequent bonding ofnew photoformed layers. This inhibited interface has been substantiallyreduced in ability to subsequently cross-link. (This interface also isstill nicely deformable, aiding in the release from a film and aiding insubsequent coating.) However, if we consider a region just slightlyfurther away from the interface within the composition, where theconcentration of inhibitor is lower (due to lower concentration ofinhibitor in the photoformable composition as a whole, and due to oxygenconsumption at the interface of the photoforming composition layerduring radical/initiator quenching and subsequent diffusion effects ofoxygen toward the interface from the remainder of the photoformingcomposition layer), the degree of cross-linking is increased due to areduction in inhibitor quenching of initiator and radicalized monomer.But there is also a greater degree of future active sites because theinterface of the photoforming composition layer absorbed some of theradiation and allowed less production of radicalized initiator andradicalized monomer to be formed during the exposure in the remainder ofthe photoforming composition layer. As we consider regions further andfurther away from the interface, in the photoforming composition layer,the same trends continue; greater degree of cross-linking due to fewerquenched radicals, and fewer radicals formed providing more futureactive sites. Also, as we consider regions further and further away fromthe interface, in the photoforming composition layer, the amount ofquenched monomer and therefore the amount of deformable composition(though no longer considered to be photoformable composition in manycases) becomes less and less causing a relatively gradual transitionfrom deformable composition to photoformed layer. This gradualtransition is very useful since it precludes chemical bonding andmechanical bonding at the interface of the photoforming compositionlayer and aids in reduction of vacuum forces that may arise during theremoval of the film from the photoformed layer. And this gradualtransition is also useful since there is now a substantially greatersurface area of potential cross-linking sites and mechanical bond sitesconnected to the photoformed layer to which subsequently applied andexposed photoformed layers may bond, thereby increasing the layer tolayer adhesion in the formed object.

It is an important distinction in this invention that the films andcoatings, which are substantially inert relative to, and which areimmiscible in, the composition, whether photoformable or photoformed,nevertheless allow the supply of permeated inhibitors through them intothe composition, and therefore can aid in both release of thephotoformed layer from the films and subsequent bonding of newphotoformed layers in regions substantially away from thefilm/coating/composition immediate interface.

The importance of the composition atmosphere in contact with thephotoformable composition becomes more apparent when a semi-permeablefilm that employs, for example, oxygen diffusion is utilized. Forexample, if the composition atmosphere is pure nitrogen, it isreasonable to assume that the photoformable composition contained in thevat on average contains less oxygen than normal, assuming equilibriumconditions. It is also reasonable that thephotoformable-composition-layer will have a sharper increase in theamount of dissolved oxygen as the semi-permeable film which diffusesoxygen is approached. And it might be expected that the photoformedlayer would also display a sharper decrease in degree of cross-linkingas the film is approached. Therefore control of the components of thecomposition atmosphere, control of inhibitors in the coatings, and/orcontrol of the imaging atmosphere, which all affect the concentration ofinhibitor within the photoformable-composition-layer, are importantelements that affect the degree of bonding of one photoformed layer toanother and the ability of a photoformed layer to be separated fromanother material through which it was exposed while in contact.

While it is preferred that the composition atmosphere be, for example,nitrogen, this in most cases is harder to control. It is possible tocontain the entire apparatus in an enclosure and to control thecomposition atmosphere to any desired extent. Such a apparatus could,for example, blow air and, for example blow extra nitrogen or oxygeninto the enclosure using a conventional blower and regulated tanks ofgas. This might be useful, since with most photoformable compositionswhen exposed using conventional methods (ie. exposing the photoformablecomposition without the use of a film or transparent plate) the extranitrogen in the composition atmosphere will increase the photospeed ofthe composition, or the extra oxygen in the atmosphere would improveinterlayer adhesion. In addition the composition atmosphere could bechanged during exposure (e.g. the composition atmosphere might compriseroughly 95% nitrogen, 5% oxygen before exposure, and the imagingatmosphere could be changed to comprise roughly 75% nitrogen, 25% oxygenduring exposure) to obtain a sharper transition from photoformed layerto deformable composition (as described above), and therefore havehigher photospeed yet good photoformed layer adhesion. It is morepreferred, however, that the composition atmosphere be air and that theconcentration of permeated inhibitor in thepermeated-deformable-release-coating be higher than that normally foundin air.

Studies were conducted, by the Applicants, with several films, Mylar®polyester, fluoroelastomer (described above), polyethylene, Teflon PFA®,and Kalrez® to determine if there was an inherently inhibiting effect onphotoformable compositions exposed in contact with and through thefilms. The tests were conducted with the film in contact with thephotopolymer on one side and air or nitrogen, as the imaging atmosphere,on the other side. Exposures were made with a mercury arc lamp from thefilm/atmosphere side into the photopolymer. In most cases where air wasthe gas on one side of the film, the hardened layer of photopolymer wassubstantially softer at the interface between the film and thephotopolymer layer produced. In cases where nitrogen was the gas on oneside of the film, the interface between the film and exposedphotopolymer was more hardened. This indicates that the film materialsthemselves may not inhibit the cross-linking ability of thephotopolymers exposed in contact with the film, but that it is thepresence of air or, more probably oxygen, which permeates through thefilm and inhibits the cross-linking ability of the photopolymer at thefilm interface during exposure.

Additional studies were performed, by the Applicants, that appear tosupport the conclusion that it is permeation of air through the filmduring exposure that inhibits the cross-linking ability of thephotopolymer, rather than the molecular structure or inherent inhibitingeffect of the film. Samples were prepared using a photopolymer whichconsisted of a formulation as detailed in DuPont's U.S. Pat. No.5,002,854 entitled "Solid Imaging Method Using Compositions ContainingCore-Shell Polymers" Example 2, hereinafter referred to as TE-1541. Thesamples were exposed using an Ultracure 100 mercury arc lamp sourcemanufactured by Efos Inc. of Mississauga, Ontario, Canada. The output ofthe light was filtered through a Corning 7-51 filter which allowstransmission of light from the lamp in a range of UV centered around 365nm. Exposures were given for around 10 seconds over an area of about 2.5in. diameter. Each sample was exposed with one surface of the followingmaterials, wetting the photopolymer and the other surface of thematerials exposed to an imaging atmosphere. The materials tested were1.0 mil polyethylene film, 1.5 mil Teflon PFA® film, 11.5 milfluoroelastomer film (as described above), 32 mil Kalrez® film, TeflonAF® coated quartz, Fluorinert™ FC-40 (perfluorocarbon) liquid, or water.Each sample was exposed with an air imaging atmosphere or a nitrogenimaging atmosphere on one side of the above materials. After exposure,the layers of photopolymer were removed from the above materials,keeping track of the layer surface in contact with the film, and cut ina strip of size appropriate for performing an IR reflectance analysisusing a BIO-RAD, Digilab Division, FTS-60 Fourier Transform InfraredSpectroscopy in reflectance scan mode. The photoformed layer sampleswere placed with the film interface side contacting a KRS-5 (ThalliumBromo-Iodide) crystal in a ATR-IR (Attenuated Total Reflectance)accessory used for measuring the spectroscopic reflectance. Inreflectance mode, this instrument is capable of outputting the spectraof the surface of a sample, from which the degree of conversion(polymerization or cross-linking) of the sample surface can bedetermined. The degree of conversion can be determined by comparing theratio of a specific wavenumber peak height above baseline, which peakheight is known to change with degree of conversion, to anotherwavenumber peak height above baseline, which is known to besubstantially unchanged by the degree of conversion. In the case ofTE-1541 photopolymer, the peak height (above baseline value) of, forexample, 811 wavenumber decreases with greater polymerization and thepeak height (above baseline value) of, for example, 1736 wavenumber issubstantially unchanged by the amount of polymer conversion orpolymerization. Therefore, in evaluating the ratio of the peak height of811 wavenumber to the peak height of 1736 wavenumber, a decrease invalue of this ratio indicates that a greater degree of conversionoccurred. As an item of comparison, the unexposed monomer (TE-1541) wasalso tested using the above evaluation method.

Following are the rankings in the test with the ranking from the mostconversion to the least conversion:

    ______________________________________                                        Exposure Contact Surface                                                                          811/1736 Wn Ratio                                         ______________________________________                                        Polyethylene Film-Nitrogen                                                                        .143                                                      Teflon PFA ® Film-Nitrogen                                                                    .185                                                      Fluoroelastomer Film-Nitrogen                                                                     .197                                                      Teflon AF ® on Quartz-Nitrogen                                                                .211                                                      Water-Air           .212                                                      Water-Air           .245                                                      Teflon PFA ® Film-Air                                                                         .252                                                      Mylar ® Film-Nitrogen                                                                         .259                                                      Water-Nitrogen      .259                                                      Kalrez ® Film-Nitrogen                                                                        .337                                                      Airorinert ™     .359                                                      Teflon AF ® on Quartz-Air                                                                     .362                                                      Polyethylene Film-Air                                                                             .376                                                      Nitrogenrt ™     .379                                                      Kalrez ® Film-Air                                                                             .420                                                      Mylar ® Film-Air                                                                              .473                                                      Fluoroelastomer Film-Air                                                                          .477                                                      Unexposed Monomer (TE-1541)                                                                       .518                                                      ______________________________________                                    

As can be seen from the above ranking, the surface of a layer exposedthrough a film that has nitrogen as the imaging atmosphere nearly alwaysshows a greater degree of conversion than does the same film if air isthe imaging atmosphere. Water, with air or nitrogen as the imagingatmosphere, shows little difference in degree of conversion sincerelatively little oxygen is soluble in water in the natural state. Andin fact, the evaluations made with water tend to indicate the amount oferror present in the test. The samples tested with Fluorinert™ liquidalso show very little difference whether the imaging atmosphere is airor nitrogen. It is believed that this is due to the fact thatFluorinert™ has a special affinity for oxygen and the oxygen must beremoved using stronger measures than just placing the liquid in anitrogen imaging atmosphere for an hour or so. However, independent oferror, a general ranking may be obtained from the evaluation giving agood indication that the imaging atmosphere on one side of a filmpermeates through the film and affects the degree of conversion of thephotopolymer during exposure. It is also important to note that thefluoroelastomer film, which is the most preferred film for the purposesof this invention, having an imaging atmosphere of air, creates anexposed photoformed layer surface adjacent to the film with the lowestdegree of conversion and exhibits the greatest difference in degree ofconversion when an exposure is made in a nitrogen imaging atmosphere.This suggests that the fluoroelastomer film has the greatestpermeability to oxygen of all films tested, yet with substantially noinherent inhibition or effect on cross-linking of the contactingphotopolymer being exposed. That is, the film material is substantiallyinert to the photoformation of the composition, however, it's ability tobe permeated by, for example, oxygen, or it's readiness to allow oxygento diffuse through it, provides a substantially inhibited surface ofdeformable composition at the interface between the film and exposedphotoformed layer, which in turn allows easier removal of the film by,for example, sliding means, or for example, peeling means. Essentially,the inhibited composition at the fluoroelastomer film surface, wheninhibited by permeated oxygen, becomes adeformable-composition-release-coating.

In the case of FIG. 2, it is preferred that, a transparentdeformable-coating-mixture 210', preferably a liquid but possibly a gel,be introduced between the plate 232 and the film 202 to ensure goodoptical coupling between the two. Even more preferable is adeformable-coating-mixture 210' that permeates the film 202 and/or is aplasticizer of the film 202. And still more preferable is adeformable-coating-mixture 210' that is of substantially similarmolecular polarity to that of the film 202 while being of substantiallydissimilar molecular polarity to that of the photoformable composition204, photoformable-composition-layer 212, and photoformed layers 222.Also, it is more preferable that such a deformable-coating-mixture 210'be of substantially low viscosity and have substantially good lubricity.It is more preferred that such a deformable-coating-mixture 210' be thesame material as the permeated-deformable-release-coating 210. And stillmore preferable that such a deformable-coating-mixture 210' tend to betransferred from the film first surface 202' to the film second surface202" by diffusion, whereby diffusion effects replenish thepermeated-deformable-release-coating 210 on the film second surface 202"should the concentration of the permeated-deformable-release-coating 210become diminished, and whereby diffusion effects no longer causetransfer of deformable-coating-mixture 210' once the concentration ofcoating is substantially the same on both the film first surface 202'and the film second surface 202". It is in the preferred case thatdiffusion provides the driving force or pressure for thedeformable-coating-mixture 210' to pass through the film 202. Anotherpreferable route would be for osmotic pressure to provide this drivingforce. Even more preferable, is a film 202 which is permeable to, forexample, air or oxygen (or other inhibitor, whether as a gas or morepreferably dissolved in solution with the coating), whereby aninhibition of photoforming of the photoformable-composition-layer 212occurs at the interface between the permeated-deformable-release-coating210 and the photoformable-composition-layer 212, and a little beyond,leaving the photoformed layer 222 deformable at this interface andforming a deformable-composition-release-coating, even after exposure,further decreasing any chemical, mechanical, hydrogen, or like bonding,and therefore providing easier sliding of the film 202 from thisinterface after exposure. It is also preferred that air or oxygen, orother permeated inhibitor 242, be substantially dissolved in thepermeated-deformable-release-coating 210 and that thedeformable-coating-mixture 210' aid in transfer of the air or oxygen, orother dissolved inhibitor 242' through the film 202 by diffusion means.It has been shown, by others familiar with the art of diffusion, thatgases penetrate more readily when they are more condensable and solublein a liquid, especially in a liquid that permeates and swells a film.This-swelling of the film, which increases the diffusion of thedeformable-coating-mixture, and in the preferred case, increases thediffusion of soluble oxygen in the deformable-coating-mixture, throughthe film, is a different transport mechanism from just capillary action,as might occur through, for example a porous fused silica plate, whichis not capable of swelling.

The presently preferred deformable-coating-mixture which has all theabove preferred properties, when used in combination with the preferredfluoroelastomer film, is Fluorinert™ FC-40 (3M, St. Paul, Minn.).Fluorinert™ Liquids are manufactured by electrolyzing an organiccompound in liquid hydrogen fluoride. The fluorination is complete.FC-40 has a molecular weight of 650. Fluorinert™ is immiscible in allphotoformable compositions tested to date, however, it can contain 37 mlof oxygen per 100 ml of Fluorinert™ without affecting the opticalclarity of the coating. The liquid is very non-polar and therefore hashigh surface tension when in contact with the typically more polarphotoformable compositions. It permeates the film quickly. Preferably,the film is first saturated with the Fluorinert™ overnight, prior toassembly in the frame. The Fluorinert™ has low viscosity and provides aslippery feel on the surface of the film. Referring to FIG. 2, in thecase of the transfer solution 211, FC-40 is preferred, however, otherFluorinert™ liquids, such as for example, FC-72 are more preferred sincethese liquids can contain a greater concentration of oxygen andtherefore enhance the diffusion of oxygen through the porous tube 238.

Following are the results of a test run with the preferred film andFC-40 in combination with TE-1541:

Approximately 20 ml of FC-40 was placed in a beaker. The fluoroelastomerfilm was stretched over the top of the beaker and clamped around theedges to form a drum. The beaker was then inverted, allowing the FC-40to be fully supported by the film in the beaker. The beaker in thisposition was placed in such a manner as to immerse the film surface,outside the beaker, in another beaker of TE-1541. The beakers were leftin this position for several months. Although FC-40 has a very highspecific gravity of 1.87 at 25° C., high surface tension when in contactwith photoformable compositions, and immiscibility with thesecompositions, the FC-40 passing through the film never accumulated atthe bottom of the TE-1541 beaker and never showed evidence of formingglobules or drops.

The Applicants' propose the following mechanisms as a possibleexplanation for the results obtained. However, this proposal is merely asuggestion, and it must be taken only as such by the reader. By no meansshould the Applicants' proposal be construed as limiting in any way thebreadth and scope of this invention. The Applicants propose that:

The FC-40 wets and swells the film very easily. Initially there is ahigh concentration of FC-40 on one side of the film. Since the film ispermeable to the FC-40 and swelled by it, diffusion effects develop andtransport the liquid to the other side of the film which is in contactwith the composition. Since there are high surface tension effectsbetween the FC-40 and the composition, the FC-40 tends to minimize it'ssurface area forming a thin coating of liquid on the composition side ofthe film. This in turn creates a high concentration of FC-40 on thecomposition side of the film, thereby substantially equilibrating theconcentration difference on either side of the film and diminishing anydiffusion and transport effects. In this way, it can be expected thatonly a thin coating of FC-40 will form on the composition side. If anyof this coating should be sloughed off during the step of sliding thefilm from the surface of the photoformed layer, the diffusion willautomatically refresh the permeated coating.

The above described self-replenishing release coating method has alsobeen tested in conditions where the FC-40 and film were at the bottom.In either case, the FC-40 permeates the film and forms a coating on thecomposition side of the film, through which an exposure can be made tocreate a photoformed layer which can then be slid on the surface of thefilm. The significance of orientation of the assembly is an importantpoint in the application of this invention. In the case described by theApplicants, a heavier liquid FC-40 was on top of the lighter liquidphotoformable composition. With this invention, the specific gravity ofthe liquid does not affect the desired results for creating a release ofa photoformed layer from the surface of the film. That is, theinvention's method of film orientation can be any method convenient forproduction of the layers or three-dimensional objects.

Any combination of film, composition and coating material mayconceivably be used in which a similar balance of properties exist. Manyplasticizers of films permeate the film and are transported through itby these methods. And many of these combinations of photoformablecomposition, film, and deformable-coating-mixture may provide adequateperformance in the production of photoformed layers andthree-dimensional objects.

Surprisingly, use of just an inhibitor, for example, air or oxygen,which permeates through a film without the presence of a coating may beused. For example, experiments have been conducted by the Applicants'that show that a film can be slid from a photoformed layer that has beenexposed with a mercury arc lamp through the film. In the Applicants'test, the fluoroelastomer film slid freely off an exposed DesoliteSLR800™ (DeSoto Chemical Corporation, Des Plains, Ill.) photopolymerlayer. The Kalrez® film exhibited a little more adhesion but could stillbe slid from the surface. The polyethylene film showed more adhesion andwould not slide from the surface but could easily be peeled off. In eachof these cases, the photopolymer surface at the film interface wasslightly tacky. An additional sample was tested using Teflon AF®(DuPont, Wilmington, Del.) FPX/FC40 which had been coated on sandblastfrosted 1/8" thick frosted quartz plate with a spiral wound #26 coatingrod, then oven heated for about 12 minutes at 160°-170° C. to evaporateoff the solvent. When the DeSoto SLR- 800™ liquid was exposed when incontact with the Teflon AF® coated side, sliding of the layer from theglass was not immediately possible, (The Teflon AF® has very low surfaceenergy and is substantially inert, however, the sandblasted surface ofthe glass telescoped through the film creating a surface that providedgood mechanical bonds. In addition, adhering the Teflon AF® to a quartzplate prevents oxygen from permeating to the interface between theTeflon AF® and the photopolymer) and the surface of the photoformedlayer was not at all tacky. The Applicants suggest that the relativefilm adhesion and surface tack of the photoformed layers issubstantially dependent on the tendency of oxygen in air to permeate thefilm and inhibit the photopolymer.

Referring to FIG. 1, use of just a film 102 with an imaging atmosphere156, such as for example, air or oxygen, which permeates through thefilm 102, diffuses into the photoformable composition 104, and whichcreates a deformable-composition-release-coating upon exposure ispossible. (To the extent that these dissolved gases are photoformationinhibiting, the inhibited composition remains deformable after exposureand is therefore acting as a deformable-composition-release-coating.)Likewise, use of just a film 102 held to a particular shape, with adeformable-coating-mixture 110' and with or without an inhibitor 142' onthe first surface of the film 102' which permeates the film 102 andcreates a permeated-deformable-release-coating 110 (and/or adeformable-composition-release-coating) on the film second surface 102"is possible. Referring to FIG. 2, when the film 202 is held to aparticular shape by a plate 232, the deformable-coating-mixture 210' ispreferred, in conjunction with dissolved inhibitors 242' since itcreates substantially improved optical coupling between the film 202 andthe plate 232 and therefore allows formation of more precise photoformedlayers 222.

It is possible to use a film that is only partially in contact with andpartially adhered to a plate. For example, one surface of the plate maybe sandblasted or in some way have a toughened surface, and the filmcould be partially adhered to the plate by, for example, an adhesive,or, for example partial melting to the high spots in the plate. Thefluorelastomer film would be particularly suitable for such anapplication since it is a thermoplastic. With this method, the filmsurface facing the composition could be smooth enough to preventmechanical bonding and allow sliding from the photoformed layer surface.The regions between the film and the plate that are not in contact wouldcreate channels through which the deformable-coating-mixture and/orinhibitors could pass to wet and permeate the film. It might be possibleto use a porous fused silica plate that would allow, for example, oxygento pass but not allow photoformable composition to pass and inhibit theinterface between the plate and the composition during exposure of aphotoformed layer. It would be preferred to improve the optical qualityof such a porous plate by utilizing a deformable-coating-mixture,capable of filling the pores of the plate, suchdeformable-coating-mixture having substantially the same refractiveindex as that of fused silica for the radiation in use. Silicone oilcompounds such as Laser Liquids™ (R. P. Cargille Laboratories, CedarGrove, N.J.) may prove useful in this application. Such a porous plate,could be made from, for example, silica frit or glass microballs, ofgood optical quality, that have been sintered together to form the plateshape. It might be preferred to, for example, use a porous fused silicaplate with a partially bonded film, such as for example, silicone films,for this method. It would be more preferred to use adeformable-coating-mixture with a dissolved inhibitor, which providessubstantially the same refractive index as that of the porous fusedsilica plate, which fills the pores in the plate, thereby improving it'soptical clarity for the wavelength in use, and which permeates the film,thereby forming a permeated-deformable-release-coating on thephotoformable composition side of the film, and also forms adeformable-composition-release-coating on the photoformed layer uponexposure thereby allowing sliding of the film/plate from the photoformedlayer surface.

FIG. 3 depicts an embodiment utilizing a porous plate 333 with poresfilled as described above by a deformable-coating-mixture 310'.Partially adhered to the porous plate 333 is a film 302, having a firstsurface and a second surface, with the film second surface 302"positioned to, at least partially, face the photoformable composition304 and the film first surface 302', at least partially, facing andpartially adhered to the porous plate 333. This porous plate 333 withpartially adhered film 302 will hereinafter be referred to as a plateassembly. In addition, the film 302 wraps around the edges of porousplate 333 assisting in containing the deformable-coating-mixture 310'.The deformable-coating-mixture 310' wets and permeates the film 302forming a permeated-deformable-release-coating 310. Above thedeformable-coating-mixture 310' and porous plate 333 is an imagingatmosphere 356, which contains an inhibitor, and which may or may not bethe same as the composition atmosphere 352, which is in contact with thephotoformable composition 304, at the composition/atmosphere interface353, within a vat 306. The imaging atmosphere 356 may diffuse into thedeformable-coating-mixture 310' forming a dissolved inhibitor 342',which then permeates through film 302 forming a permeated inhibitor 342.Also, within the vat 306 is a platform 320, which is translated in adirection substantially normal to the film second surface 302", duringthe production of photoformed layers 322, by platform translation means324. Plate assembly translation means 319 (shown just as an arm witharrows for the sake of clarity) translates the plate assembly anddeformable-coating-mixture 310' in a direction substantially parallel tothe film second surface 302". Radiation source 314 exposes thephotoformable-composition-layer 312 through a photomask 316, thetransparent deformable-coating-mixture 310', the film 302, the porousplate 333, and the permeated-deformable-release-coating 310 in much thesame manner as described in other Figures. It would be preferred in thepractice of this embodiment, when the deformable coatings are in theform of a low viscosity liquid, that the plate assembly be substantiallyhorizontal.

In operation, the plate assembly would initially be positioned over theplatform 320 forming a photoformable-composition-layer 312 between theplatform 320 and the permeated-deformable-release-coating 310. Radiationsource 314 would then be turned on creating radiation imagewise to passthrough photomask 316, the deformable-coating-mixture, the plateassembly, the permeated-deformable-release-coating, and intophotoformable-composition-layer 312, thereby creating a photoformedlayer 322 and a deformable-composition-release-coating due to thepresence of permeated inhibitor 342. After exposure, the plate assemblywould be translated by plate assembly translation means 319, separatingthe film 302 from the surface of layer 322 and allowing newphotoformable composition 304 to flow into this region of separation.After the separation is complete, the platform 320 and the photoformedlayer 322 are translated a distance of at least onephotoformable-composition-layer 312 from the plate assembly. Next, theplate assembly is positioned above the platform 320 and previousphotoformed layer 322 forming a new photoformable-composition-layer 312between the permeated-deformable-release-coating 310 and the previousphotoformed layer 322. The imagewise exposure, separation, platformtranslation and recoating steps would continue as above until a completethree-dimensional object is fabricated.

It is preferred for the production of three-dimensional objects that theexposure by radiation be performed imagewise, which image represents alayer of a three-dimensional object. And it is preferred that the firstexposure step, as described above, be adequate to create adhesionbetween portions of a photoformed layer and a platform, thereby ensuringsubstantial support for the layer, ensuring substantial subsequentstatic registration with the imagewise radiation, and ensuringcontrolled relative position between the previously photoformed layerand the film surface, between which the photoformable-composition-layerwould exist. It is further preferred that subsequent exposure steps beadequate to ensure adhesion between portions of the photoformablecomposition being exposed and portions of the surface of a previouslyexposed photoformed surface. The presently preferred exposure methodutilizes UV light exposure through or reflected from an appropriatephotomask, however, other radiative exposure methods, such as, forexample, direct writing using a focused scanning laser beam, x-rays,microwave or radio-frequency wave excitation, and the like may be used,assuming such radiation induces photoforming of the photoformablecomposition. Photomasks useful for the practice of this invention may besilver halide films. (either transmitted through or backed by a mirrorand reflected through), liquid crystal cells (reflective ortransmissive), electrostatically deposited powders on a transparent web,ruticons, etc.

It has been found by the Applicants that the use of a focused beam froma relatively high power laser as the exposure source yields results thatcreate more adhesion of the photoformed layer to films through whichthey were exposed when air is the imaging atmosphere. The Applicantsbelieve this is due to the polymerization rate outrunning the inhibitionrate. Use of thinner films, faster inhibitors, or for example, moreconcentration of oxygen, and/or, for example, oxygen saturatedpermeated-deformable-release-coatings would be preferred since theywould substantially decrease the adhesion of the films to photoformedlayers.

Sliding of the film, and more preferably the film, plate and coatingsassembly, from the surface of a photoformed layer is preferred to reducethe build-up of vacuum forces that might occur during separation of thefilm and photoformed layer. Even more preferred, would be sliding thefilm, or assembly, to a region where there is a substantially sharpchange in the shape of the film, or assembly, such that the surface ofthe film is no longer parallel to and moves sharply away from thephotoformed layer surface, allowing the photoformable compositionsubstantially unrestricted flow into the region where the photoformedlayer and film separate. It is preferred that such a substantial changein film shape, for an assembly, occur at the edge of the plate. And asshown in FIG. 2, it is most preferred that such film 202 shape changeoccur as a recess 228 ground into or originally formed in the plate 232,which recess 228 is deep enough to allow substantially unrestricted flowof composition 204 into the region where the film 202 and photoformedlayer 222 separate.

Occasionally, during the practice of the preferred invention, it may benecessary to perform a replenishing step which involves re-saturatingthe film with the deformable-coating-mixture. Typically during thisstep, the vacuum pressures which draw the deformable-coating-mixturefrom between the film and the glass are relieved and excessdeformable-coating-mixture is pumped or allowed to flow into thisregion. Even more preferable is to first bubble air or pure oxygenthrough the deformable-coating-mixture in a separate flask, therebyre-saturating the deformable-coating-mixture with dissolved inhibitorand then to allow this (inhibitor saturated) deformable-coating-mixtureto re-saturate the film. The Applicants suggest that this re-saturationstep may be necessary as often as every ten exposures. However, thisdepends substantially on, for example, the amount of exposure provided,the area of the layer being imaged and, for example, the type ofphotoformable composition in use. In the preferred method as shown inFIG. 2, where an exposure and recoating ofphotoformable-composition-layer 212 occur each time the layers pass overa recess, it is even more preferred that the film 202 and plate 232 oneach side of the recess region 228 create two separate chambers 250' and250 so that when one side provides the exposure step, the other side isbeing re-saturated.

Pre-saturating the film prior to assembly allows the system to be usedsooner and avoids loss of tension in the film due to film swelling,however this step is not required. It is preferred that thedeformable-coating-mixture be introduced between the film and the platea few hours before use to allow the deformable-coating-mixture topermeate the film. The Applicants have found that the presence ofphotoformable composition on the proper side of the film substantiallyspeeds the diffusion process and the creation of apermeated-deformable-release-coating. The deformable-coating-mixtureneed not be placed under pressure to aid the diffusion process, thoughthis is possible. Typically, the deformable-coating-mixture isintroduced into the region between the glass and film using Just headpressures, however, many kinds of pumps or, for example, pressurechamber devices, or for example, bladder pumps may be used. It ispreferred to draw the deformable-coating-mixture from the film and glassafter permeation using vacuum since this causes the film to tightlyregister with the glass during the imaging step. The vacuum is usuallycreated by drawing the air or oxygen from a chamber that contains thedeformable-coating-mixture and is connected to thefilm/glass/deformable-coating-mixture assembly. However, any vacuummethod, well known in the art may be used. Since, thedeformable-coating-mixture in the preferred method is FC-40 which has ahigh specific gravity, even the use of low head pressures may be used todraw the deformable-coating-mixture out. When thedeformable-coating-mixture is drawn out between the film and the glass,there is still a substantial amount of deformable-coating-mixture leftbetween the two. This is due to viscosity and flow resistance effectsthat compete with the drawing out vacuum.

After the exposure step, sliding of the assembly, parallel to the secondfilm surface and relative to the previously formed layers, can beperformed prior to translation of the platform and layers one or morelayer thickness away from the plate. It is preferred, however, to firsttranslate the platform and previously formed layers away one layerthickness prior to sliding of the assembly. It may be possible totranslate the platform away from the plate more than one layer thicknessand then move the platform back to a one layer thickness position duringeach layer formation step, but this is not preferred. If a roughenedplate or a porous fused silica plate, with a partially adhered film isused, however, it is preferred that the sliding translation occur priorto platform translation.

The special materials of construction usually chosen as shown in FIG. 2that have not been described heretofore are listed as follows. This inno way should be perceived as a limitation of possible materials thatcould be used rather the information is being provided to aid others ofordinary skill in the art to construct such an assembly:

Tube Screen- Aluminum, steel or copper screen, with sharp points removedor turned inward, which has been rolled to the proper diameter and sewn,soldered, or brazed at the seam.

Flexible Tubing- Tygon® Tubing (VRW Scientific, San Francisco Calif.)

Translation Means- Unidex XI motor controller, ATS-206-HM-6" TravelPositioning Motor Driven Stage W/Stepper Motor and HomeMarker,(Aerotech, Pitts. Pa.).

What is claimed is:
 1. An apparatus comprising:a) a substantiallytransparent, composition-inert, composition-impermeable, semi-permeablefilm, having a first surface and a second surface, said first surfacebeing positioned to partially contact an imaging atmosphere capable ofpermeating said film, and said second surface being positioned topartially contact a photoformable composition; b) means for creatingimagewise radiation through said film in order to form a photoformedlayer and a deformable-composition-release-coating at said film secondsurface; and c) means for separating said film from said photoformedlayer.
 2. An apparatus as recited in claim 1 wherein said film is ofsubstantially different molecular polarity than that of saidcomposition.
 3. An apparatus as recited in claim 1 wherein said film isa fluoroelastomer film.
 4. An apparatus as recited in claim 1 whereinsaid imaging atmosphere comprises air.
 5. An apparatus as recited inclaim 1 wherein said imaging atmosphere comprises oxygen in a greaterconcentration than normally found in air.
 6. An apparatus as recited inclaim 1 further comprising:means for forming additional layers ofphotoformable composition on previous photoformed layers.
 7. Anapparatus as recited in claim 6 further comprising:a) a tenter frame forholding said film to a shape; b) frame assembly translation means fortranslating said tenter frame and film slidably; c) a platforms locatedto adhere to said photoformed layers; and d) platform translation meansfor moving said platform.
 8. An apparatus as recited in claim 7 whereinsaid film is positioned to be permeated by a deformable-coating-mixtureand dissolved inhibitors.